Signs of Winter 10: Delicious Microbial Ecosystems

Photo by J. Hamilton

I have to admit something: I love bread. I think that I could give up almost any other food more easily than bread. The very thought of not having bread (for breakfast, lunch and/or dinner) makes the meals feel incomplete and inadequate.

I have kept up with the growing nutritional literature that clearly shows that calories from carbohydrates (all those sugars!) are more likely to contribute to fat deposition (insulin is the mediator of this reaction!). Much of the blame for our obesity epidemic seems to be attributable to excessive carbohydrate ingestion. I do try to limit my sugar consumption from soft drinks (I avoid them), candy and cookies (I try to be disciplined) and prepared foods (is corn syrup in everything?), but bread, really good bread, and especially homemade bread, is something that I will not give up easily.

Both of my kids agree with me (only Deborah has any restraint on bread consumption in our immediate family!). Marian and Joe gave me a bread maker for Christmas, in fact, and I have been working my way through my bread cookbook making Challah, honey bread, Vienna bread, Swiss egg bread, whole wheat bread, and more several times a week. What an amazing invention! I wish that they would come up with a comparable “beer machine” so that I could as easily add homemade ale to my regular diet.

No, come to think of it, it is probably better that beer making is as time consuming and laborious (all of that washing and sanitizing!) as it is.

As part of our new, family bread making tradition, Marian bought three packages of sourdough starter from a company based in San Francisco and gave Joe and I each one for Christmas (and kept one for herself). We decided to each start our sourdough cultures at the same time in our respective corners of America (Seattle, Albuquerque, and Apollo, PA) and then compare the breads that we eventually make.

Photo by M. Hamilton

We all began our starters (which we will call our “sponges” from now on) within a few days of each other. Joe (in Seattle) and I (in Apollo) had an immediate problem with temperature. The mixture of water, bread flour and the provided packet of dried yeast and bacteria spores had to be incubated at 85 degrees! There was nowhere in Joe’s apartment or in our house that was 85 degrees this time of year! The packet instructions, though, suggested that you turn on your oven light and put the sponge container into the closed oven. Joe tried it and I followed suit, and it works!! We’ll figure out how to replace a worn out oven light later (I hope that it is not too expensive!)! All of our sponges, though, were happily bubbling away and giving off whiffs of alcohol and sour yeast. The sourdough, microbial ecosystem was established.

So what all was going on here? Why did we have to “feed” the fermenting brew every day for a week or more? Why was the texture and consistency of the sponge changing so much? What the heck was in that little dry pack of starter?

To answer these questions in reverse: the packet contained up to seven species of wild yeast and up to five species of lactobacilli bacteria (the classic sourdough microbial array!). These yeasts and bacteria have been identified as the “sourdough agents” responsible for the distinctive San Francisco sourdough bread! The yeasts (which are, of course, unicellular fungi that are able to live in both aerobic and anaerobic environments) first break down starches in the flour to mixtures of simple sugars and disaccharides (like sucrose and maltose) and then start to work on the simple sugars and the sucrose making lots of carbon dioxide in the process (all that bubbling!). The bacteria then start working in particular on the maltose (yeast are apparently “maltose intolerant”) and break it down to lactic acid and acetic acid (significantly dropping the pH of the system!) and the process make more carbon dioxide. There are hints of other organic acids in the scent coming off the sponge (not always pleasant odors!), but these scents change and mellow as the days go by (less butyric acid and more acetic acid, I am sure!).

There is an intense battle for space and food resources between the starter yeast and bacteria species and the yeasts and bacteria that were just riding along in the flour (or had just dropped into the system from the surrounding air!). Different locations will make different microbial contributions to the sponge (hence the Hamilton experiment across the country!). The starches of the flour are being rapidly broken down (which explains the sudden liquefaction of the sponge), and this food source needs to be replenished daily (hence the daily “feeding” of the sponge with fresh flour and water). The liquid portion of the sponge, by the way, is called “hooch” (that seems appropriate based on its smell).

Photo by M. Hamilton

The yeasts and the bacteria populations swing wildly up and down, but, eventually, reach an equilibrium and form a relatively stable community. All of this takes an active week or so of feeding and fussing (all at 85 degrees F!), and, then, finally, the sponge is ready to use in bread!

When making bread the added sourdough sponge yeast and bacteria will break down some of the starches in the bread flour and produce the carbon dioxide that acts as the leavening agent to make the bread rise! The sponge will also contribute many of the acids and other exotic flavors from its complex microbial community to give the sourdough its unique flavor. Often regular bread yeast is added to the mix just to make sure that sufficient carbon dioxide of produced to make the brad light and fluffy. Too much added yeast, though, can breakdown the flavors of the sourdough sponge.

I have made two loaves of sourdough bread so far. The complex sourdough flavors were only faintly detectable in the first loaf but much more robust in the second. The texture of both loaves, though, was incredible!

Lactobacilli bacteria like the ones in sourdough are also the major microbial agent in making yogurt! A particular species (Lactobacillus bulgarius (also called “Lactobacillus acidophilis”)) mixed with Streptococcus thermophiles break down the lactose (a disaccharide) in milk generating lactic acid in the process. These acids then denature the milk proteins causing curdling (thickening) of the milk (thus forming yogurt!). The breakdown of the lactose makes the food easier to digest and the acidic environment prevents other bacteria from growing in the yogurt (thus preserving it!). Another great use of bacteria!

I am going to have a slice of bread and some yogurt for breakfast! Go microbial ecology!


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2 Responses to Signs of Winter 10: Delicious Microbial Ecosystems

  1. Mardelle Kopnicky says:

    It is called the staff of life for a reason! Enjoy your creations .

  2. Nancy Burns says:

    You make the bread and I will help you eat it! I totally agree there is nothing better than good bread! (and beer)!

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